The term “electrotransport” refers generally to the delivery or extraction of an agent (charged, uncharged, or mixtures thereof) through a body surface (such as skin, mucous membrane, or nails) wherein the delivery or extraction is at least partially electrically induced or aided by the application of an electric potential. The electrotransport process has been found to be useful in the transdermal administration of many drugs including lidocaine, hydrocortisone, fluoride, penicillin, and dexamethasone. A common use of electrotransport is in diagnosing cystic fibrosis by delivering pilocarpine iontophoretically. The pilocarpine stimulates production of sweat. The sweat is then collected and analyzed for its chloride content to detect the presence of the disease. Electrotransport devices generally employ two electrodes, positioned in intimate contact with some portion of the animal's body (e.g., the skin). A first electrode, called the active or donor electrode, delivers the therapeutic agent (e.g., a drug) into the body. The second electrode, called the counter or return electrode, closes an electrical circuit with the first electrode through the animal's body. A source of electrical energy, such as a battery, supplies electric current to the body through the electrodes. For example, if the therapeutic agent to be delivered into the body is positively charged (i.e., cationic), the anode is the active electrode and the cathode is the counter electrode to complete the circuit. If the therapeutic agent to be delivered is negatively charged (i.e., anionic), the cathode is the donor electrode and the anode is the counter electrode.
A widely used electrotransport process, electromigration (also called iontophoresis), involves the electrically induced transport of charged ions (e.g., drug ions) through a body surface. Another type of electrotransport, called electroosmosis, involves the trans-body surface (e.g., transdermal) flow of a liquid under the influence of the applied electric field. Still another type of electrotransport process, called electroporation, involves forming transiently existing pores in a biological membrane by applying high voltage pulses. In any given electrotransport system, one or more of these processes may occur simultaneously to some extent.
Most transdermal electrotransport devices have an anodic and a cathodic electrode assembly, each electrode assembly being comprised of an electrically conductive electrode in ion-transmitting relation with an ionically conductive liquid reservoir which in use is placed in contact with the patient's skin. Gel reservoirs such as those described in Webster U.S. Pat. No. 4,383,529 are the preferred form of reservoir since hydrated gels are easier to handle and manufacture than liquid-filled containers. Water is by far the preferred liquid solvent used in such reservoirs, in part because many drug salts are water-soluble and in part because water has excellent biocompatability, making prolonged contact between the hydrogel reservoir and the skin acceptable from an irritation standpoint.
The term “agent” is intended to have its broadest interpretation and is used to include any therapeutic agent or drug, as well as any body analyte, such as glucose. The terms “drug” and “therapeutic agent” are used interchangeably to refer to any therapeutically active substance that is delivered to a living organism to produce a desired, usually beneficial, effect. This includes therapeutic agents in all the major therapeutic areas including, but not limited to: anti-infectives such as antibiotics and antiviral agents; analgesics, including fentanyl, sufentanil, buprenorphine and analgesic combinations; anesthetics; anorexics; antiarthritics; antiasthmatic agents such as terbutaline; anticonvulsants; antidepressants; antidiabetic agents; antidiarrheals; antihistamines; anti-inflammatory agents; antimigraine preparations; antimotion sickness preparations such as scopolamine and ondansetron; antinauseants; antineoplastics; antiparkinsonism drugs; antipruritics; antipsychotics; antipyretics; antispasmodics, including gastrointestinal and urinary; anticholinergics; sympathomimetrics; xanthine derivatives; cardiovascular preparations, including calcium channel blockers such as nifedipine; beta blockers; beta-agonists such as dobutamine and ritodrine; antiarrythmics; antihypertensives such as atenolol; ACE inhibitors such as ranitidine; diuretics; vasodilators, including general, coronary, peripheral, and cerebral; central nervous system stimulants; cough and cold preparations; decongestants; diagnostics; hormones such as parathyroid hormone; hypnotics; immunosuppressants; muscle relaxants; parasympatholytics; parasympathomimetrics; prostaglandins; proteins; peptides; psychostimulants; sedatives; and tranquilizers.
Of particular interest in transdermal delivery is the delivery of analgesic drugs for the management of moderate to severe pain. Control of the rate and duration of drug delivery is particularly important for transdermal delivery of analgesic drugs to avoid the potential risk of overdose and the discomfort of an insufficient dosage. One class of analgesics that has found application in a transdermal delivery route is the synthetic opiates, a group of 4-aniline piperidines. These synthetic opiates, e.g., fentanyl and certain of its derivatives such as sufentanil and remifentanil, are particularly well-suited for transdermal administration. These synthetic opiates are characterized by their rapid onset of analgesia, high potency, and short duration of action. They are estimated to be 80 times(fentanyl) and 800 times (sufentanil), more potent than morphine. These drugs are weak bases, i.e., amines, which are primarily cationic in acidic media.
Electrotransport devices use at least two electrodes, an anode and a cathode, that are in electrical contact with some portion of the skin, nails, mucous membrane, or other surface of the body. One electrode, commonly called the “donor” electrode, is the electrode which is used to deliver the agent into the body. The other electrode, typically termed the “counter” electrode, serves to close the electrical circuit through the body. For example, if the agent to be delivered is positively charged, i.e., a cation, then the anode is the donor electrode, while the cathode is the counter electrode which serves to complete the circuit. Alternatively, if an agent is negatively charged, i.e., an anion, the cathode is the donor electrode and the anode is the counter electrode. Additionally, both the anode and cathode may be considered donor electrodes if both anionic and cationic agent ions, or if uncharged dissolved agents, are to be delivered.
Furthermore, electrotransport delivery systems generally require at least one reservoir or source of the agent to be delivered to the body. Examples of such donor reservoirs include a pouch or cavity, a porous sponge or pad, and a hydrophilic polymer or a gel matrix. Such donor reservoirs are electrically connected to, and positioned between, the anode or cathode and the body surface, to provide a fixed or renewable source of one or more agents or drugs. Electrotransport devices also have an electrical power source such as one or more batteries. Typically at any one time, one pole of the power source is electrically connected to the donor electrode, while the opposite pole is electrically connected to the counter electrode. Since it has been shown that the rate of electrotransport drug delivery is approximately proportional to the electric current applied by the device, many electrotransport devices typically have an electrical controller that controls the voltage and/or current applied through the electrodes, thereby regulating the rate of drug delivery. These control circuits use a variety of electrical components to control the amplitude, polarity, timing, waveform shape, etc. of the electric current and/or voltage supplied by the power source. See, for example, McNichols et al., U.S. Pat. No. 5,047,007.
To date, commercial transdermal electrotransport drug delivery devices (e.g., the Phoresor, sold by Iomed, Inc. of Salt Lake City, Utah; the Dupel Iontophoresis System sold by Empi, Inc. of St. Paul, Minn.; the Webster Sweat Inducer, model 3600, sold by Wescor, Inc. of Logan, Utah) have generally utilized a desk-top electrical power supply unit and a pair of skin contacting electrodes. The donor electrode contains a drug solution while the counter electrode contains a solution of a biocompatible electrolyte salt. The power supply unit has electrical controls for adjusting the amount of electrical current applied through the electrodes. The “satellite” electrodes are connected to the electrical power supply unit by long (e.g., 1-2 meters) electrically conductive wires or cables. The wire connections are subject to disconnection and limit the patient's movement and mobility. Wires between electrodes and controls may also be annoying or uncomfortable to the patient. Other examples of desk-top electrical power supply units which use “satellite” electrode assemblies are disclosed in Jacobsen et al., U.S. Pat. No. 4,141,359 (see FIGS. 3 and 4); LaPrade, U.S. Pat. No. 5,006,108 (see FIG. 9); and Maurer et al., U.S. Pat. No. 5,254,081.
More recently, electrotransport delivery devices have become much smaller, particularly with the development of miniaturized electrical circuits (e.g., integrated circuits) and more powerful light weight batteries (e.g., lithium batteries). The advent of inexpensive miniaturized electronic circuitry and compact, high-energy batteries has meant that the entire device can be made small enough to be unobtrusively worn on the skin of the patient, under clothing. This allows the patient to remain fully ambulatory and able to perform all normal activities, even during periods when the electrotransport device is actively delivering drug. Such small self-contained electrotransport delivery devices are disclosed for example in Tapper, U.S. Pat. No. 5,224,927; Sibalis, et al., U.S. Pat. No. 5,224,928; and Haynes et al., U.S. Pat. No. 5,246,418.
Reference is now made to FIG. 1 which depicts an exploded view of an exemplary electrotransport device 10 having an activation switch in the form of a push button switch 12 and a display in the form of a light emitting diode (LED) 14. Device 10 comprises an upper housing 16, a circuit board assembly 18, a lower housing 20, anode electrode 22, cathode electrode 24, anode reservoir 26, cathode reservoir 28 and skin-compatible adhesive 30. Upper housing 16 has lateral wings 15 which assist in holding device 10 on a patient's skin. Upper housing 16 is generally composed of rubber or other elastomeric material, such as an ethylene vinyl acetate copolymer having 28% vinyl acetate (EVA-28). Lower housing 20 is typically composed of a plastic or elastomeric sheet material (such as, e.g., polyethylene terephthalate glycol (PETG) or polyethylene) which can be easily molded or thermoformed to form cavities and is then cut to form openings therein. Printed circuit board assembly 18 comprises an integrated circuit 19 coupled to discrete electrical components 40 and battery 32. Circuit board assembly 18 is attached to housing 16 by posts (not shown in FIG. 1) passing through openings 13a and 13b, the ends of the posts being heated/melted in order to heat stake the circuit board assembly 18 to the housing 16. Lower housing 20 is attached to the upper housing 16 by means of adhesive 30, the upper surface 34 of adhesive 30 being adhered to both lower housing 20 and upper housing 16 including the bottom surfaces of wings 15.
On the underside of circuit board assembly 18 is a battery 32, which may be a button cell battery, such as a lithium cell. The circuit outputs of the circuit board assembly 18 make electrical contact with the electrodes 24 and 22 through openings 23, 23′ in the cavities 25, 25′ formed in lower housing, by means of electrically conductive adhesive strips 42, 42′. Electrodes 22 and 24, in turn, are in direct mechanical and electrical contact with the top sides 44′, 44 of drug reservoir 26 and electrolyte reservoir 28. The bottom sides 46′, 46 of reservoirs 26,28 contact the patient's skin through the openings 29′,29 in adhesive 30. Upon depression of push button switch 12, the electronic circuitry on circuit board assembly 18 delivers a predetermined DC current to the electrodes/reservoirs 22,26 and 24,28 for a delivery interval of predetermined length.
Electrotransport delivery devices are prepared, shipped and stored (or stored, shipped and stored), prescribed and then used. As a result, the devices must have components that have extended shelf lives that, in some instances, must comply with regulatory requirements. For instance, the U.S. Food and Drug Administration has shelf life requirements of from six to eighteen months for some materials. One complicating factor in achieving an extended shelf life is the dimensional stability of EVA-28 when exposed to elevated temperatures. In order to achieve satisfactory dimensional stability of the device housing when it is manufactured from EVA-28, for example, the molding conditions must be carefully optimized, thus limiting the processing window. Otherwise warpage as well as unacceptable dimensional changes will occur at temperatures as low as 40□C. If the device housing should encounter excessive heat during storage or shipping, however, these same undesirable dimensional changes can occur. Further, electrotransport delivery devices typically contain electronic components (e.g., integrated circuits), conductive circuit traces and electrical connections therebetween which can corrode or otherwise be degraded by water or water vapor. Unfortunately, devices such as device 10 shown in FIG. 1 have hydratable or hydrated reservoirs 26, 28. Thus, humidity or moisture from the hydrated reservoirs can permeate through the device housing during manufacturing and storage, which can thus cause corrosion of the electronic components within the device, thereby reducing the shelf life of the device. One source of permeation is around the electrical leads or contacts which must supply electric current and voltage from the battery into the relatively wet environment of the reservoir housing.
In order to apply voltage from a power source to the agent reservoir, there must be some method or device used to place the power source in electrical communication with the drug reservoir.
One method is to mold or punch a hole in the plastic housing used to contain the reservoir gel. An electrode is then placed on the outside of the housing covering the hole. The gel is then placed within the reservoir cavity so that electrical contact can be made with the electrode through the hole in the housing.
There are several critical points in the implementation of this method. All of which involve sealing the hole in the reservoir housing. Because the reservoirs gels are largely water, liquid and/or moisture can escape from housing and corrode the electronic components if there is not proper sealing between the electrode and the housing and the housing and the gel and the housing. Because these devices are shipped and stored in sealed pouches, any moisture leaking from the reservoir may get trapped in the interior of the device and expose the controller circuitry to the water. Water, particularly water containing electrolyte salts such as found in a reservoir gel, can be very corrosive and quite damaging to the device.
One solution has been to develop dry or non-hydrated electrodes. See for example U.S. Pat. Nos. 5,158,537; 5,288,289; 5,310,404; and 5,320,598. Because the gel matrix only needs to be hydrated during actual use by the patient during drug delivery, the device can be manufactured and stored with the reservoir in a dry or non-hydrated state. Then a hydrating liquid, with or without the agent to be delivered contained within the liquid, is added to the reservoir just prior to use. But this approach is not without its own engineering challenges.
Another approach has been to make the device resistant to the moisture and corrosion. One step that has been taken to combat the corrosion problem has include gold plating the contact tabs and circuit board traces. Such solutions are inherently expensive and add additional steps to the manufacturing process.